1. Field of the Invention
This invention relates to sharing of data in a distributed processing system, and more particularly to the transmission, processing and storage of real time data in a network system.
2. Background Information
In most computer networks, data transmitted over a data highway interconnecting the various stations in the network is addressed to a specific station or stations. The message is ignored by the remaining stations on the network. The network interface at the addressed station interrupts the station central processing unit which then processes the message. Often the receiving station sends back an acknowledgment to the sender station. In these systems, the message identifies both the receiving and sending stations. Such a process is efficient in an application with interactive communication needs between stations.
In broadcast multi-cast networks, the messages are not addressed to any specific station. Each station receives all of the data transmitted and traditionally takes what it needs. This also requires processing of the message by the central processing unit of the receiving station. Typically, to reduce the burden on the system, data is only broadcast by exception. That is, only when the value of a piece of data changes is a message sent. Thus, for instance, in a distributed process control system, where various functions are being performed by a number of stations on a network, data is only broadcast when the value of a variable changes. Other deterministic systems, such as automatic teller machines linked to a central unit by a network also only send data when there is a transaction to process. However, such systems can become overburdened if there is a large disturbance in the process being controlled, or a large number of transactions occur simultaneously.
Assignee of the present invention has developed a broadcast network in which data from the various stations are bundled into packets or blocks of data which are transmitted periodically, whether or not the data has changed. Data with a short latency is transmitted at a fast repetition rate, while other data which is less critical or changes at a slower rate, is transmitted at more widely spaced time intervals. In this system, all the data is transmitted repetitively and is received by all of the stations. Each station examines each block of data received and slices off for storage only that data which it needs. This system is designed for the worst case scenario, and thus does not become overwhelmed by large disturbances in the system. However, local processing of each block of data is required to determine the data to be stored in memory at that station, which limits the data rate that can be handled by the system.
There is a need, therefore, for an improved broadcast network system with an enhanced data rate and yet which does not become overwhelmed by the worst case scenario. Additionally, peer-to-peer communications should also be provided without compromising the real-time performance.